This invention relates to a nuclear reactor sensing system; and more particularly to a hydroball string sensing system that determines the location and velocity of a hydroball string.
To control the operation of a nuclear reactor the neurron flux within the reactor core region is monitored. To monitor this neutron flux, numerous tubes are positioned within the core. These tubes house strings called hydroball strings that include stainless steel beads on a flexible stainless steel cable. Each of the stainless beads includes a material such as manganese that absorbs neutrons while the stainless steel bead is in the core region.
After the strings have been in the core for several minutes, the strings are removed from the core region and the decay time of the activated manganese in each bead is measured. This measurement indicates the neutron flux to which each bead was subjected while within the reactor core region. The hydroball strings are moved into and out of the reactor core region by pumping water through the tubes in the direction of desired hydroball string movement.
With this technique for approximating the neutron flux in a reactor core region, it is critical: (1) to know how long the hydroball string spends in the reactor core region, (2) to know how much time elapses between the string leaving the core region and the start of measuring the radiation emitted from each hydroball, and (3) to confirm the location of the hydroball string at various times as it is moved into and out of the reactor core region. Because the hydroball string is housed within a thick walled stainless steel tube that contains reactor core fluid at the same pressure as within the reactor core, it is difficult to achieve these critical objectives.